1. Field of the Invention
The present invention relates to a system for automatically reading film information, particularly film sensitivity, provided on a film cartridge in what is called the DX system. The DX system has been developed to enable film information such as film sensitivity and the number of frames in be automatically set to a camera when the film cartridge is loaded into a cartridge chamber.
2. Description of the Prior Art
The film cartridge used in this system, as will be described in detail later, comprises a peripheral wall including film information code patterns into which the film information is encoded by arranging conductive areas and non-conductive areas according to patterns corresponding to the film information. The cartridge chamber includes a plurality of electric contacts arranged therein for contacting the film information patterns. When the film cartridge is loaded into the cartridge chamber, the film information such as film sensitivity is read through conductive and non-conductive states between the electric contacts provided by the film information code patterns. These code patterns, called CAS code patterns, are standardized. The film information code patterns representing film sensitivity are arranged as shown in FIG. 1.
Notations "E1" to "E6" in FIG. 1 indicate positions of code areas as counted from an end of the film cartridge from which a film winding shaft projects. Thus, the code area referenced "E1" is hereinafter called a first code area, the code area referenced "E2" a second code area and so on. The hatched portions represent conductive areas, and the blank portions represent non-conductive areas. "SV" represents film sensitivity (speed value) according to the APEX system.
It is old in the art to read film information by detecting conduction and non-conduction between the first code area and the other code areas. To meet the needs for compact cameras, however, it may be necessary to dispose a different mechanism in a position which otherwise provides a space to accommodate an electric contact for contacting the first code area. Then this contact loses its accommodating space.
The Japanese patent publication Kokai No. 61-107329, for example, discloses a system for automatically reading film sensitivity from film information code patterns without using the first code area. This system comprises two electric contacts for contacting each of the code areas except the first code area. One of the electric contacts is positive, and the other is grounded, namely negative. This pair of contacts is contactable with the same code area, whereby the film sensitivity is read on the basis of conductive and non-conductive states thereof.
According to this publication, as shown in FIG. 1, a line of demarcation for the fourth code area is drawn between ISO 320 and ISO 400, to allocate conductive areas for ISO 320 and below and non-conductive areas for ISO 400 and above. Furthermore, films of ISO 100 sensitivity and ISO 400 sensitivity are in wide use and other films are seldom used. Accordingly, a simple improvement is proposed to provide a pair of electric contacts only for the fourth code area for detecting the sensitivity to be ISO 400 in the event of conduction between the two contacts and ISO 100 when no conduction occurs therebetween.
The above technique of detecting sensitivity on the basis of conduction and non-conduction between the pair of electric contacts for contacting the same code area requires no electric contact for the first code area, thus allowing the space for accommodating the electric contacts to be reduced axially of the film winding shaft. This technique, therefore, has an advantage over the older technique which, for example, includes a reference electric contact for contacting the first code area which is constantly conductive regardless of film sensitivity. With this technique, the sensitivity is detected on the basis of conduction and non-conduction between the reference contact and other contacts which contact the other code areas. In particular, the proposed improvement mentioned above requires only a space corresponding to a width of the fourth code area axially of the film winding shaft.
However, the technique of detecting sensitivity on the basis of conduction and non-conduction between one pair of electric contacts for contacting one code area has the following drawback:
It is necessary to provide a sufficient space between two electric contacts forming a pair in order to avoid detection errors due to a direct contact therebetween. This is achieved by arranging the two electric contacts so that they are contactable with the corresponding code area adjacent opposite ends thereof instead of positions adjacent its center. It is then necessary to fix the contacts to appropriate positions with high precision in order to avoid detection errors due to a displacement of the film cartridge causing the electric contacts to contact a code area next to the code area for which the contacts are intended. This not only lowers the efficiency of assembly work, but is prone to cause the electric contacts to contact a next code area as a result of a film cartridge displacement even if the electric contacts are fixed with high precision.
Accordingly, a system has been desired which is capable of reading film information without necessitating one pair of contacts for each code area even where, for some reason, a contact cannot be provided for the first code area.
the following examples represent the type of film information reading system noted in the outset hereof, and in particular, represent the type of mechanism surrounding the electric contacts.
One such example is disclosed in U.S. Pat. No. 4,582,408. This mechanism comprises a base plate disposed peripherally of a cartridge chamber to be movable radially of the cartridge chamber, and pins supported by the base plate to be movable radially of the cartridge chamber. The pins project inwardly of the cartridge chamber to have proximal ends contactable with a peripheral wall of a film cartridge loaded in the cartridge chamber. Springs are also provided to urge the base plate and pins inwardly of the cartridge chamber. The distal ends of the pins define electric contacts.
Another such example is disclosed in Japanese Patent Publication Kokai No. 60-225121. In this example, segments formed of a resilient material are arranged peripherally of a cartridge chamber to be movable radially of the cartridge chamber. The segments have free distal ends projecting into the cartridge chamber for contacting a peripheral wall of a film cartridge loaded in the cartridge chamber. The free ends of the segments define electric contacts.
In the former case, three components, i.e. the pin, base plate and spring, are required to provide an electric contact. Furthermore, this mechanism requires means for holding the pin against disengagement from the base plate toward the inside of the cartridge chamber and for holding the base plate against disengagement in the same direction from a camera body. In addition, the spring must be placed in a narrow space between the pin/base plate and the camera body. These requirements result in a complicated overall construction and a low efficiency of assembly work.
The latter example has the advantage of constructional simplicity and higher assembling efficiency since the electric contacts are provided merely by attaching the segments. The free ends of the segments are movable to retracted positions by being pushed radially of the cartridge chamber. However, these free ends do not oscillate to the retracted positions when pushed axially of the film winding shaft. This results in the following inconvenience.
Generally, the winding shaft of the film cartridge is fitted onto a rewinding shaft of a camera when loading the film cartridge into the cartridge chamber. Thus, the loading of the film cartridge involves a movement thereof axially along the direction of the winding shaft. In the course of loading the film cartridge into the cartridge chamber, therefore, one end corner of the film cartridge slides axially along the peripheral wall of the cartridge chamber and tends to contact the projecting free ends of the segments. In this prior construction, the free ends of the segments do not retract radially outwardly of the cartridge chamber when the corner of the film cartridge pushes the free ends axially along the direction of the winding shaft. As a result, the corner of the film cartridge becomes caught by the free ends of the segments to obstruct the film cartridge loading.